Campbell Scientific FP2 data

The FP2 data format uses 16 bits to represent a variable-precision floating point number. FP2 has a total range of -7999 to 7999 and variable precision of 0.001 to 1. It also has the ability to signal +/– INF and NAN, most commonly used to indicate a computational or measurement error. FP2 range and maximum precision shows the numeric ranges and precision; Bit description describes the bits, and Calculation of finished value provides bit usage in calculating a finished value.

 

Bit description
Name	Bit	Description
Sign (S)	16 (MSB)	Specifies the sign of the value. 0 = positive, 1 = negative.
Exponent (E)	15 and 14	Specifies the magnitude of the negative decimal exponent.
Mantissa (M)	13 to 0 (LSB)	Specifies the magnitude of the 13-bit mantissa, 0 to 8191

 

Calculation of finished value
Sign (S)	Exponent (E)	Mantissa (M)	FP2 value equals
0	00	8191	+ INF
1	00	8191	– INF
1	00	8190	NAN
0 or 1	00 or 01 or 10	0 to 7999	(–1 ^ S) × (10 ^ –E) × M

When transmitted in a pseudobinary format, the 16 bits are encoded as follows. Bits 16 through 13 are the least significant four bits of the first byte, bits 12 through 7 are the least significant six bits of the second byte, and the last six bits are the least significant bits of the last byte. The following tables are examples of encoding values.

Encoding of 1234
Character 1 = @								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	0	0	0	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of 1.234
Character 1 = F								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	0	1	1	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of 12.34
Character 1 = D								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	0	1	0	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of 123.4
Character 1 = B								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	0	0	1	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of 0.123
Character 1 = F								Character 2 = A								Character 3 = {
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	0	1	1	0	0	1	0	0	0	0	0	1	0	1	1	1	1	0	1	1

 

Encoding of -1234
Character 1 = H								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	1	0	0	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of -1.234
Character 1 = N								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	1	1	1	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of -12.34
Character 1 = L								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	1	1	0	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of -123.4
Character 1 = J								Character 2 = S								Character 3 = R
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	1	0	1	0	0	1	0	1	0	0	1	1	0	1	0	1	0	0	1	0

 

Encoding of -0.123
Character 1 = N								Character 2 = A								Character 3 = {
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	1	1	1	0	0	1	0	0	0	0	0	1	0	1	1	1	1	0	1	1

 

Encoding of INF
Character 1 = A								Character 2 = ?								Character 3 = ?
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	0	0	0	1	0	0	1	1	1	1	1	1	0	0	1	1	1	1	1	1

 

Encoding of -INF
Character 1 = I								Character 2 = ?								Character 3 = ?
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	1	0	0	1	0	0	1	1	1	1	1	1	0	0	1	1	1	1	1	1

 

Encoding of NAN
Character 1 = I								Character 2 = ?								Character 3 = ~
				Sign	Exponent		Mantissa			Mantissa								Mantissa
p	1	0	0	b16	b15	b14	b13	p	1	b12	b11	b10	b9	b8	b7	p	1	b6	b5	b4	b3	b2	b1
0	1	0	0	1	0	0	1	0	0	1	1	1	1	1	1	0	0	1	1	1	1	1	0